Lighter fasteners for aircrafts

boeingAerospace industry needs lighter fasteners. Slic Pin, designed by Pivot Point Inc., employs a spring-loaded plunger to replace the nut and cotter pin. The plunger retracts when inserted into the stack up and once clear, springs up and locks into place. The Slic Pin is ideal for holes with limited access for placing cotter pins. The bolt reduces the need for tools and comes in eight different basic shank diameters ranging from 0.181 to 0.746 inches. A removable plunger option is also available; it features a rounded top when the pin needs to be removed.

Rivets are mainly used to fasten aerospace skins to the sub-structure of the aircraft. On that front, Cherry Aerospace designed the Cherry 1900 Bulbing Blind Rivet, its own version of the NAS1900 rivet. Thanks to the rise of composite structures, the NAS1900 rivet has become a popular option for rivet fasteners. The Cherry 1900 forms a large blind-side footprint, suiting it for such structures. The rivet also includes the Cherry Shift Washer, which provides a more consistent installation in the stackup and extends tool life. The Cherry rivet comes with a protruding head or a 100-deg. flush head. Minimum shear strength is based on the material chosen for the sleeve. A-286 sleeve offers shear strength of 1090 to 2400 lbs., while the Monel sleeve offers 1020 to 2260 lbs. The rivet itself is A-286 Cres.

Stripping of threads is a major problem on aircraft. Due to engine-induced vibrations and the turbulence on the wings and airframe, nuts start to lose their torque, threads start to grind away, and nuts fall off.

Spiralock, from Stanley Engineered Fastening, is a thread form that helps prevent loosening due to vibration and eases load distribution. Unlike the standard 60-deg. angle of standard threads, Spiralock uses a 30-deg. angle. Using a modified angle enables uniform load distribution, reducing the load on the first thread engagement and thus minimizing the likelihood of thread stripping. The Spiralock also generates a higher radial thread loading, lowering the chances of shear failure.

A higher torque of 10% to 20% is required compared to a standard thread. Testing on a 1/4-28 Spiralock fasteners, when compared to a similar regular fastener, revealed fatigue life was enhanced by 300%. Spiralock threads can be found in Stanley’s hex flange nuts, self-clinching nuts, threaded inserts, wire thread inserts, and key-locking threaded inserts. Made-to-order fasteners featuring the Spiralock threads are also available from Stanley.

Read also: Aero-Lite threaded fasteners from Alcoa

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